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Physicist John Harris to deliver Hofstadter Lecture on origin of hot 'quark soup'

By Maria José Viñas

John Harris

In the beginning, there was an extremely hot, dense soup. Just 10 millionths of a second after the Big Bang, the universe consisted of a plasma of tiny particles called quarks and gluons that was 100,000 times hotter than the center of the sun. That quark-gluon plasma is the origin of all the matter that we know today.

Yale physicist John W. Harris will talk about this amazing primordial state of matter during this year's Robert Hofstadter Memorial Lecture at 8 p.m. Monday, April 30, in Room 200 of the Hewlett Teaching Center in the Science and Engineering Quad. The title of his talk, which is free and open to the public, is "What Is That Black Hole Doing in My Quark Soup?" He also will give a more technical colloquium, titled "Evidence for a Quark-Gluon Plasma in the Laboratory," at 4:15 p.m. Tuesday, May 1, in Room 201 of the Hewlett Teaching Center.

"Everything that we don't understand [about the origin of the universe] happened in the first 10 millionths of a second," says Harris. "And we are trying to understand what the matter in the universe was at that time and to determine its properties."

Harris, who is a professor of physics and leader of the Relativistic Heavy Ion Group at Yale, will discuss the importance of studying this hot soup to understand the origins of the universe.

"Up until some 30 years ago or so we were stuck with what we knew from standard nuclear physics," Harris says. "We just knew that nuclei and atoms existed, and looking back in time we couldn't get past a few minutes after the Big Bang."

But now, powerful tools like the Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC), which began operating in 2000 and where Harris does research, allow physicists to look further back toward the birth of the universe. Even though the researchers have yet to claim discovery of the quark-gluon plasma, they are confident they have created it, Harris says.

Quarks are fundamental particles that are tightly bound together by gluons into groups of three to form protons and neutrons, which are the building blocks of the nuclei of atoms. Quarks are never found alone in nature. The RHIC smashes two beams of gold nuclei traveling almost at the speed of light to produce a super-hot fireball, hot enough in its core to provide the energy necessary to free the quarks.

Harris says that the experiments at the RHIC have allowed physicists to observe some surprising properties of the quark-gluon plasma. The main one is that this primordial state of matter, which physicists believe still exists in the cores of stars, behaves like a liquid. Besides, Harris says that recently string theorists have been able to describe some of the unusual properties of the liquid by placing a black hole in the middle of the "quark soup."

The Yale professor is the 14th speaker chosen for the lecture series hosted by the Stanford Physics Department to commemorate the late Nobel Prize-winning physicist Robert Hofstadter, who was a member of the Stanford faculty from 1950 until his death in 1990. Harris is a fellow of the American Physical Society and has been both a collaborator and a founding spokesperson for an experiment at Brookhaven National Laboratory called STAR, for Solenoidal Tracker At RHIC.

In his lecture, Harris will talk about the next episode in the quark-gluon plasma hunt, which will take place in Switzerland at the Large Hadron Collider of the European Organization for Nuclear Research (CERN). In an experiment called ALICE (A Large Ion Collider Experiment), scientists will begin accelerating heavy nuclei in 2009. At CERN they expect to produce and study hotter conditions with 30 times higher energy than at RHIC and possibly vaporize the liquid, Harris says.

Harris is the leader of the U.S. team that will participate in ALICE. Twelve American institutions, including Yale, Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory, will build one of the components of the experiment. In total, more than 1,000 scientists from 104 institutions in 30 countries are participating in the experiment.